>>406
Please try it as it will be reproduced 100%.

NG pattern1
01) Lock and equip an item (e.g. A)
02) Open a treasure chest
03) Equip a newly acquired item (e.g. B)
04) Lock the "B"
05) Unlock the "A"
06) Dismantle all unlocked items
07) The "B"'s equip comes off

NG pattern2
01) Lock and equip an item (e.g. A)
02) Open a treasure chest
03) Unlock the "A"
03) Equip a newly acquired item (e.g. B)
04) Lock the "B"
06) Dismantle all unlocked items
07) The "B"'s equip comes off

OK pattern1
01) Lock and equip an item (e.g. A)
02) Open a treasure chest
03) Lock a newly acquired item (e.g. B)
04) Equip the "B"
05) Unlock the "A"
06) Dismantle all unlocked items
07) The "B"'s equip is kept

Unlocking new items and equipping them in a different order will change the results.